1. Field of the Invention
The present invention relates to a driving circuit for a liquid crystal display (hereinafter, referred to as LCD), and more particularly to a column line driving circuit for an active matrix LCD.
2. Description of Related Art
FIG. 4 shows an example of the structure of the active matrix LCD. In FIG. 4, a LCD panel 102 is constituted by two-dimensionally arranging liquid crystal cells (pixels) 101 in a matrix shape. On the periphery of this LCD panel 102, there are provided a vertical driver 103 for selecting rows, and a horizontal driver (hereinafter, referred to as column line driving circuit) 104 for selecting columns. As regards the column line driving circuit 104, it has heretofore been arranged only on the upper side of the LCD panel 102 as shown in the same figure, or the same one each is arranged on both the upper and lower sides thereof, and each driving circuit has been adapted to correspond to the entire range of signal voltage applied to the LCD.
In the conventional column line driving circuit constructed as described above, however, since each driving circuit is to cover a minimum level to a maximum level of signal voltage, the dynamic range is large.
In order to produce a column line driving circuit with such a large dynamic range, transistors with low threshold voltage Vth must be used, and it is difficult to constitute the column line driving circuit by transistors with such high threshold voltage Vth as a polysilicon TFT (Thin Film Transistor). Moreover, since the number of circuit elements is great, it is very difficult to realize using such an element with a large variation in characteristics as polysilicon TFT. Also, even in case where it is produced using monocrystal silicon, a circuit (for example, push-pull circuit) having sufficient driving ability must be used for both input and output of current, and therefore, both circuit area and current consumption will be increased.